This invention relates to an apparatus for processing a broken wire electrode in a wire-cut electric discharge machine equipped with the function of returning a wire electrode, following the breakage thereof, to a fixed point such as a machining starting point or the position at which the wire broke. More particularly, the invention relates to an apparatus for processing a broken wire electrode in a wire-cut electric discharge machine equipped with a memory for storing the position of wire breakage, means for generating a movement command which retracts a workpiece from the breakage position after the wire breaks, means for positioning the workpiece at a predetermined rethreading position on the basis of the command, and means for positioning the workpiece at the breakage position after the wire electrode is rethreaded in the wire transfer system.
A wire-cut electric discharge machine establishes a voltage differential between the wire electrode and a workpiece to induce an electrical discharge in the intervening space. The machine moves the workpiece relative to the wire electrode on the basis of machining command data, whereby the workpiece is cut into the desired shape owing to the electrical discharge as the workpiece moves. In an electric discharge machine of this type, there are occasions where the wire electrode breaks within the workpiece when the applied voltage, workpiece feed speed and other machining conditions are improper during the electric discharge machining operation. To repair the wire electrode following breakage, the operator pulls the wire electrode upwardly through a lower guide, rethreads it through a groove cut in the workpiece, and attaches it to a take-up mechanism via an upper guide. The lower guide is a hindrance, however, and the narrow width of the cut groove makes it difficult to pass the wire electrode through the groove. Accordingly, it is ordinary practice to move the workpiece or wire electrode manually by a jog-feed to bring a starting bore of a large diameter, provided in the workpiece, into coincidence with the wire electrode position in a horizontal plane, and then thread the broken wire electrode through the starting bore and attach it to the take-up mechanism via the guide member. When the broken wire electrode is repaired in this fashion, considerable labor is required to bring the wire electrode position within the horizontal plane into coincidence with the starting bore by the manual feed operation. Consequently, there is a decline in machining efficiency since a considerable period of time is required following wire breakage to rethread the wire in the wire electrode transfer system and execute electric discharge machining from the position of wire breakage.
Accordingly, an object of the present invention is to provide an apparatus for processing a broken wire electrode in a wire-cut electric discharge machine in which, when the wire electrode breaks, the wire electrode can be rethreaded in the wire electrode transfer system and electric discharge machining can be resumed from the breakage position in a short period of time.